Portable electronic devices and micro-electro-mechanical-systems (“MEMS”) are conventionally powered by batteries. With the advancing sophistication of such devices, and an ever increasing need for more power, improvements have been made to the shelf life, efficiency and overall useful life of batteries in recent years. Rechargeable batteries, such a lithium ion and lithium polymer (“Li-Poly”) batteries, are also in widespread use due to their reliability, relatively high power output and comparatively long useful life.
While rechargeable batteries have a much longer useful life than those which cannot be recharged, an obvious limitation of their use is that they must be periodically recharged. Depending on the extent of use, even modern lithium ion and Li-Poly batteries may need to be recharged on a daily basis or every two to three days. This presents a problem in the field, such as for those portable electronic devices and MEMS used by the military and others, where a ready source of electrical power to recharge batteries may not be available for days at a time.
U.S. Pat. No. 6,613,972 discloses a portable micro-generator system designed to generate electrical power which employs a micro-combustor that operates with hydrocarbon fuel. Propane, butane or methylacetylene combined with air is supplied to the micro-combustor where it is burned within a combustion region to produce heat. One or more internal walls of the micro-combustor are formed of a thermoelectric material which is capable of producing electrical energy when exposed to a temperature differential. This temperature differential is created by directing a flow of incoming, cooler air-fuel mixture, and the heated exhaust gas produced from combustion, past opposite surfaces of the thermoelectric material.
Micro-generators of the type disclosed in the '972 patent have an efficiency in converting thermal energy to electrical energy on the order of about 5%. This limits the amount of electrical energy which can be obtained from the device, and therefore restricts its usefulness in directly powering portable electronic devices and MEMS, or in providing electrical energy to recharge batteries used in such devices. Additionally, fuel consumption can become an issue given such a low conversion efficiency. Consequently, the micro-generator of the '972 patent has limited practical application in its present form.